The traditional reliability of telecommunication systems that users have come to expect and rely upon is based, in part, on the reliance on redundant equipment and power supplies. Telecommunication switching systems, for example, route tens of thousands of calls per second. The failure of such systems, due to either equipment breakdown or loss of power, is unacceptable since it may result in a loss of millions of telephone calls and a corresponding loss of revenue.
Power plants employable in standby applications (e.g., telecommunications, UPS applications) address the power loss problem by providing the system with an energy reserve (e.g., a battery) in the event of the loss of primary power to the system. Power plants employable in other applications (e.g., cyclic, photovoltaic or automotive applications) may likewise require an energy reserve in the event the primary power is insufficient (or unavailable) to power the entire system. For example, in cyclic applications, the energy reserve may be employed to supplement the primary power during periods of peak usage.
A power plant that powers telecommunications systems commonly includes a number of batteries, rectifiers and other power distribution equipment. The primary power is produced by the rectifiers, which convert an AC main voltage into a DC voltage to power the load equipment and to charge the batteries. The primary power may, however, become unavailable due to an AC power outage or the failure of one or more of the rectifiers. In either case, the batteries then provide power to the load. Redundant rectifiers and batteries may be added to the power plant as needed to increase the availability thereof.
The power plant commonly employs lead-acid batteries (e.g., valve-regulated lead-acid (VRLA) batteries) as the energy reserve. The batteries are typically coupled directly to the output of the rectifiers and may instantly provide power to the load in the event an AC power outage occurs. During normal operation, the batteries are usually maintained in a fully charged state to maximize a duration for which the batteries can provide energy to the load equipment.
As a battery ages, however, its capacity or energy-storage capability decreases thereby reducing a duration for which the battery can provide energy, even when fully charged. In many applications, particularly telecommunications applications, the battery is considered to have failed when its actual capacity has fallen below a threshold, such as 80% of its rated capacity (for some telecommunications applications). A failed battery should be replaced in an orderly fashion to maintain the availability of the power plant. It is crucial, therefore, to be able to assess whether the capacity of a particular battery has fallen below its threshold.
An accurate method for assessing the capacity of the battery is to fully discharge the battery. Completely discharging the battery to assess the capacity, however, may present major disadvantages. If an AC power outage occurs during or after the discharge test, but before the battery has been fully recharged, the full energy reserve provided by the battery will not be available. This obviously jeopardizes the availability of the power plant and the reliability of the telecommunications system (or other systems) powered therefrom. Further, since a battery may only be charged and discharged a finite number of times, each cycle of complete discharge and charge necessarily reduces the overall life span of the battery.
Other methods, such as an ohmic technique or a partial discharge coupled with algorithmic calculations, may also be employed. Although these methods may be conveniently performed and may be relatively quick when compared to the full discharge method, these methods have not proven to be highly accurate.
Accordingly, what is needed in the art is a system and method for assessing the capacity of a battery that provides an accurate measurement of the battery's capacity in a short amount of time yet maintains the availability of the power plant at a satisfactory level.